DESCRIPTION (provided by investigator): The purpose of this project is to examine the relationship of substance use to HIV risk behavior among adolescents in their first sexual encounters compared to more recent encounters. Reviews of studies of substance use and condom use in specific sexual encounters suggest that drinking is associated with nonuse of condoms or other contraception at first intercourse, but not in other kinds of sexual encounters. Moreover, most of these event-level studies have not examined separately the effects of alcohol and drug use. In this project, we propose to use the National Longitudinal Study of Adolescent Health (Add Health), a large, nationally representative study of adolescents in grades 7 to 12, to investigate the role of drinking and other drug use in the use of condoms and other contraceptives in first and recent sexual encounters. We will: 1. Describe and compare patterns of drinking, other drug use, and condom use in the first sexual experience and the most recent sexual experience. 2. Use multilevel statistical techniques to assess the association of substance use and contraceptive use in these events. 3. Investigate potential reasons for any differences that occur in the role of substance use and risk behavior in first vs. more recent experiences of intercourse, including the age of the respondent and the amount of sexual and drinking experience.